Lead-purifying process



March 1931- J. B. SCHUETTENHELM 1,794,647

LEAD PURIFY ING PROCES S Filed March 31, 1950 Mn: lNVENTOR BY Mfi MORNEY i Patented -Mar. 3, 1 931 YUNIT'ED STATES PATENT OFFICE 1 JOHN B. scnuarrannmm, or xnnnoeo, IDAHO, assreivoa 'ro BUNKER mm. a sumvan mine a GONGENTRAT-ING comm, or KELLOGG, IDAHO, A coaroaarron LEAD-summits rnocnss equal efficiency either before or after soft-' emn W i th respect to common lead bullion, which must later be de-silverized, it is important to previously eliminate or reduce the copper content as far as possible as this is a great advantage in the subsequent removal of gold and silver. Gold and silver are removed by zinc and if the'copper is not previously re- .moved, more zinc must be employed in the de-silverization than would be necessary if the co per had not been eliminated. Further, i copper is present in the de-silverizing process, the gold-silver-zinc dross will 0bvi-. ously contain at least a moiety of copper which latteris detrimental in the subsequent refining of both gold and silver.

The presence of either copper or arsenic or both in antimonial lead or common lead bullion constitutes an impurity that results in penalizing dockage of the lead product under f present market requirements,and such prodso not will command a correspondingly'higher price dependent 'upon the extent to which theseimpurities are eliminated. Of course lead contains many other foreign substances some of which are valuable by-products,'when removed, and some of which are worthless and which are'impurities in-fact.

It is the primary object of this invention to provide an improved process whereby copper and arsenic can be removed from either anti- 4 monial leadbullion or common lead bullion to such neghglble extent as to avoid dockage entirely, or practically so.

My improved rocess is essentially of the drossin type an is carried out with the mass 1n a mo ten state and subjected to circulation of a prescribed character such as will successively immerse the dross downwardly from, and'then restore it to the surface, subsequent to each of a plurality of sln'mming recovery operations, this feature of the invention servstructure 6, which leaves the kettle acce sible.

ing to reduce the lead content of the skimmings. The temperature of the molten mass may be gradually reduced as the process proceeds, and because of the-fact that copper and arsenic are both of lighter specific gravit than lead, this temperature reduction whic may be made in a single stage, serves to freeze the former and thereby increases impurity recovery. 4

A feature of primary im ortance consists in a reagent that has a su cient affinity for copper and arsenic to cause separation of the same from the lead and thereby render these impurities free to be dressed at the surface in a manner to facilitate the operations of skimmiflg off these impurities with a minimum loss of lead, and in the most improved form of the invention this reagent is, or consists of ammonlum chloride.

A further feature of this novel reagent is that it functions selectively by separating copper and-arsenic from the lead without separating gold, silver and many other foreign substances thereby very greatly faclhtating the subsequent de-silverizing process.

The invention hasmany other ob'ec-ts and features which will be more fully escribed in connection with the accompanying drawing and which will be more partlcularly pointed out in and by the appended claims.

In the a companying drawing, I have shown in vertical section an apparatus for carrying. out the process of this invention.

In the drawing, I have showna drossing kettle 1, disposed in' brickwork 2, having suitable outlets 3. A burner 4, provides a controllable source-of heat for the kettle 1- However, this structure is merely suggestive andany like expedient may be employed in substitution thereof, within the province of. my invention.

. Superimposed on the flanges 5, of the kettle 1, and spanning-the latter, is a beam on opposite sides of the former. Re erence will next be made to a means for .difiusin the reagentthroughout the mass in supported by hangers 8, from the beam strucand will be substantially constant, and the dlsposition of the casing 7, is such that its upper or ingress end 9, will be below the level A, and-the lower or egressing end 10, will be at a substantial depth in the mass, as shown. Within and near the egress end 10, of the casing 7 I have shown a circulating means which may be in the form of a propeller having a hub 11, secured to shaft 12. Attached to said hub 11, are blades 13, canted to exert a downward thrust on the mass as the propeller is rotated in one direction. The lower end of shaft 12 may be journalled in a bearing 14, and the upper end is shown journalled in a bearing 15, mounted on beam 6. A gear 16, on shaft 12, is shown in mesh with a gear 17 on shaft 18, suitably journalled in a bearing 19, and to which shaft 18, power may be applied in any suitable manner, causi g rotation of'the propeller in one directionl It will now be clear from the fdregoing, and by reference to the arrows, that when the propeller is rotating, the mass will be drawn radially inwardly near the surface and forced downwardly through the casing and the mass will then move radially outwardly and upwardly to compensate for displacement of the surface mass. Therefore, the dross will be successively immersed downwardly from the surface thereby intermingling with the mass, and the next dross formed will'afford a new content of impurities. However, it will be clear that the above circulating movement of the mass, alone and unaided by a reagent, Would not be either practical or effective.

Having described a desirable form of apparatus, I will next describe one manner in.

which the process may be performed, first W1th common lead bullion.

Common lead bullion may be transferred directly from the lead blast furnace to the kettle 1, the bullion having a temperature of approximately twelve hundred degrees F. (1200 deg. At this temperature, the lead bullion contains a considerable propor tion or quantity of impurities dissolved, or alloyed, having of course a lead content there- 1n. Such impurities are composed chiefly of copper, arsenic, zinc, iron, bismuth and sulphur.

It may be noted that at this stage or temperature, the copper and zinc are probably to a great extent in the form of sulphides, as copper sulphide and zinc sulphide, although a percentage of these elements may be present in metallic form, as for instance, antimony, arsenic and bismuth. The bullion also contains precious metals, namely, gold and silver. The copper content in this blast furnace common lead bullion is approximately one percent" (1%) and arsenic will be present in a proportion of about twenty-five hundredths .25 0 Of c ourse at this high temperature of 1200 degs. F., it is not necessary to employ the burner 4, or any source of heat, in fact, the mass now in the kettle 1, is either cooled or allowed to cool to about eight or nine hundred degrees F., at which latter temperature, either after, or withoutpreviously operating the propeller, an initial dross will form on the surface when the mass is quiescent. Further, this initial dross forms, without the aid pf a reagent. Hence, the impurities in the inltial dross are those, primarily, which are free, but

impregnated with lead.

This initial dross is skimmed off and it contains the greatest percentage of copper, and as a result of this initial skim, the copper content in the lead mass is reduced to about fifteen hundredths (15%) percent, and the arsenic is reduced to about twenty-two hundredths (22%) percent, which elimination is of course far from sufiicient to render the lead profitably marketable. As gold, silver and bismuth are not recovered by this process, and obviously are not removed from the mass by this initial dross and skim, no reference need be made to either and their relative content in the molten mass will remain the same as it initially was.

I will next describe the next or second step in the process which involves the use of my novel reagent. At this point it is informative to state that while in some cases the temperature of the mass may be gradually lowered and a succession of drossings and skims made to complete the recovery of impurities, is is not absolutely essential to the success of the invention, as in actual practice, I have obtained equally good results by cooling, the

lead bullion almost to the freezing point and making recovery in a single treatment operation, which is an obvious advantage over any other process known to me.

Thus, assuming that the mass has been allowed to cool in the kettle 1, almost to the freezing point of the lead bullion, and with a content of the latter of ninety five tons (95 tons) I add to the lead bullion about thirty (30) pounds of sal ammoniac and start the propeller to thoroughly diffuse the reagent throughout the molten mass. Then the propeller is arrested to allow the mass to become quiescent, and the copper and arsenic, which have been separated'by the reagent from the lead, will dross at the surface primarily because of the fact that both are of lighter spe- I bullion to about one hundredths (01%) and 130 the arsenic content will be reduced from twenty-two (22%) hundredths percent, as in the initial lead bullionto about ten hunilredths (.10%) percent, in the final lead bulion. In cases where I have performed the process by gradually reducing the temperature of the mass and makin a series of dosages of the reagent, and afiternately skimming, I foundthat in the first reagent skim, the dross contained about five (5%) percent copper and about three (3%) percent arsenic. In the final drossing, the dross contained about three (3%) percent copper and about six (6%) percent arsenic, a decrease of the former and an increase of the latter in the successive drosses.

It is both informative and important to state that in the total process, the quantity of dross skimmed off will be only about two. or three tons, from a mass of ninety five tons of bullion. To the best of my knowledge and belief, this process involves a smaller quantity of dross, for the copper and arsenic recovery, than any process known to me.

Reference will next be made to the treat 'ment of antimonial lead bullion.-

Antimonial lead is transferred directly from the blast furnace to the kettle in a 80 manner similar to common lead bullion. The initial dross is also taken off in a similar manher while the mass is cooling to 800 degrees, or in fact, if the mass is cold, it will be disposedin the dressing kettle 1, and its temperature will be raised to about 800 or 900 degrees F., to reduce the mass to a molten state, and may if desired, although not necessarily, be gradually cooled or reduced in temperature while the rocess is carried out. If the process is carried out in stages or steps, the propeller will be operated, after a dosage of the reagent, to difluse the reagent thruout the mass, and then the propeller will be arrested to permit the impurities to drossat the'surface and be skimmed off, as will now be understood, this operation', or operations continuing in successive order until the mass cools beyond any possibility of recovery of the impurities. The total amountof the reagent for this bullion, is substantially the same as with common lead bullion. As with common lead bullion, the treatment of antimonial lead hun- In practicing the invention with antimon- .dross and skim ranged from one (1%) percent to three (3%) percent. The quantity of dross removed was about three tons from .eighty five tons of antimonial lead bullion.

I used substantially twenty five pounds of reagent for eighty-five tons of lead bullion. This antimonial lead bullion contains eighteen (18%) percent antim'ony,,one (1%) percent copper and ten (10%) hundredths percent arsenic, before treatment with this process.

of co 'per and arsenic, and. also the weight of the ross, are given in approximate figures as precisely the same results cannot be obtained in all operations because of varying conditions which cannot 'be controlled to a precise degree.

It will be understoodthat the percentages grees F., which is, of course, much higher than the melting point of lead. The melting point of arsenic is diflicult to determine as arsenic volatilizes when subjected to heat without going through the stageof becoming liquid, and hence, it is impossible to determine what itdoes when in solution with molten lead. V

As previously stated, my novel. reagent consists of what is commercially known as Sal Ammoniac, and which is chemically known as ammonium chloride.

This substance constitutes a reagent for the function described, of the greatest potency and which can be used either in a gaseous or solid form, the latter being preferable be- .cause it is more readily handled. The low cost, relatively speaking, together with the relatively small quantity necessary are of material importance, andthe latter feature, alone, illustrates its effectiveness.

The great potency of. this reagent, to the best of my knowledge and belief, 1s due to its intensive aflinity for both copper and arsenic, whereby each'isso quickly and almost completely separated from the lead as to surpass in efliciencyall other reagents I have ever known-or used.

Because this reagent, and its constituents,

are volatile-when subjected to the hot mass,

it does not leave, or add, any matter deleteri= ous to either the lead or the dross.

. A further feature of importance is that this reagent is selective in its function, having an aflinity for copper and arsenic but not for gold or silver. Hence, in the case of common lead bullion, whichanust be subsequently de-silverized, the revious removal of cop or by this process,,w1thout affecting the gol or silver, is very beneficial. This is due to the fact that when the gold and silver are subsequently removed by zinc, the almost total absence of copper does not interfere with subsequent refining treatment of these precious metals.

While I have disclosed one specific embodiment of the invention, I do not wish to be limited thereto except for such limitations as the claims may import.

I claim:

1. Theherein-described process of recovering copper and arsenic in the form of dross from hot impure lead to purify the latter, comprising, skimming ofi' the initial dross of a molten mass of lead,'in causing the molten mass constantly to circulate downwardly from and upwardly to the surface in endless paths to successively cause the dross to sink from and then ascend to the surface, in introducing a charge of ammonium chloride into the circulating molten mass to separate the copper and arsenic from the lead whereby both the former will rise by upward currents and gravity tothe surface, in skimming off the dross to recover the copper and arsenic content thereof with the mass quiescent, and in repeatedly and alternately introducing charges of the ammonium chloride and circulating and ceasing to circulate the mass, and in gradually reducing the temperature of the mass as the process proceeds to freeze the copper and arsenic and thereby facilitate isolation of the same due to their relatively higher melting points as compared to lead, whereby the dross will gradually become drier as the process proceeds.

2. The herein-described process of recovering copper and arsenic in the form of dross from hot impure lead to purify the latter,

comprising, causing the molten mass of lead to circulate downwardly from and upwardly to the surface to successively cause the dross to sink from and then ascend to the surface, in introducing a charge of ammonium chloride into the clrculating molten mass to separate the copper and arsenic from the lead, in allowing the lead to cool, and in skimming off the dross when the mass is quiescent to recover the copper and arsenic.

In witness whereof, I have hereunto set my hand.

J. B. .SCHUETTENHELM. 

